Probing Forster and dexter energy-transfer mechanisms in fluorescent conjugated polymer chemosensors

Fluorescence quenching in solutions of a pendant-functionalized conjugated polymer chemosensor (ttp-PPETE) has been evaluated in the presence of a variety of transition metal cations, including Ni2+, Co2+, Cu2+, Fe2+, and Cr6+. Photophysical analysis of the emission quenching revealed a static quenching mechanism that demonstrated strong positive deviations from predicted linear behavior. The enhanced emission quenching mechanism was found to correlate closely with the relative loading of the cationic analytes on the polymer chemosensor. This behavior has been attributed to rapid energy transfer along the polymer backbone. A modified Stern-Volmer static quenching model has been successfully applied that incorporates an energy-transfer term that takes into account different energy-transfer mechanisms. Both Forster and Dexter energy-transfer enhancements were observed for ttp-PPETE quenching depending upon the identity of the quencher analyte involved. Stern-Volmer constants in all cases were on the order of 10(5) M-1 for the transition metals reported. Photophysical characterization for ttp-PPETE includes absorbance, emission, and single-photon counting lifetimes in the absence and presence of varying concentrations of the analytes.